Soil structure characteristics, functional properties and consistency limits response to corn cob biochar particle size and application rates in a 36-month pot experiment

The particle size (PS) and application rate (RA) of biochar influence soil-biochar interaction with concomitant effects on soil chemical and physical properties. However, limited studies exist that quantify how biochar PS and RA, acting solely or together affect soil structure characteristics and functional properties. This study investigated the effect of PS and RA of corn cob biochar on soil water retention (SWR) and aeration indicators such as relative gas diffusivity, structural characteristics such as pore size distribution and pore organisation, and consistency limits of a tropical sandy clay loam soil. A pot experiment was conducted using two biochar PSs (<2 and 2-4 mm) and four biochar RAs of 0, 20, 40 and 80 Mg ha-1. Both intact soil cores (100 cm3) and disturbed bulk soil samples were collected after 36 months of amendment for measurements of soil chemical and hydraulic properties, and consistency limits. Biochar application of 80 Mg ha-1 significantly (P < 0.05) increased soil organic carbon and SWR. However, plant available water was neither affected by biochar PS nor RA. Further, biochar PS and RA acting solely or together did not significantly modify air permeability, consistency limits and estimated soil pore continuity, organisation and tortuosity. Further studies are needed to confirm whether the overall lack of significant changes in these soil properties after 36 months of amending with corn cob biochar also pertains to other biochar feedstock and soil types. Such information is useful in selecting suitable biochar amendments that improve soil conditions for crop growth.